An actuator is known from U.S. Pat. No. 4,263,487. This actuator has a primary shaft having a tension lever of twin-armed configuration, which primary shaft can be rotated manually to and fro between two end settings by hand via a crank handle. A delivery shaft, which is provided with a twin-armed drive lever and can be rotated to and fro between a disconnect and a connect setting, runs parallel to the primary shaft. Between the arms of the primary shaft and delivery shaft there is respectively disposed a compression spring of a spring-loading arrangement. The compression springs, given that the input and delivery shafts are parallel to each other, mutually counterbalancing their pre-tension. The delivery shaft is held the disconnect and connect setting counter to the force of the compression spring which can be tensioned upon the respective rotation of the primary shaft by means of a connecting or disconnecting latch acting upon the drive lever. Shortly before the primary shaft reaches the corresponding end setting, the tension lever runs into the latch concerned in order to release the drive lever and hence the delivery shaft. Following the completion of the switching maneuver, the drive lever then runs parallel again to the tension lever. For the realization of an opposite switching maneuver, the primary shaft is rotated in the opposite direction, as a result of which the other compression spring for the actuation of the delivery shaft is tensioned.
A disadvantage with this actuator is that a dedicated compression spring is respectively required for the connection and disconnection. Furthermore, the connect and disconnect setting of the delivery shaft cannot be reliably achieved by the force of the compression springs, since in these settings the effect of the two compression springs is cancelled out.
A further actuator is disclosed in DE-C-32 17 255. The primary shaft is connected via a pair of gearwheels to an intermediate shaft parallel thereto. This supports a one-armed tension lever and the likewise parallel delivery shaft possesses a drive lever. The tension lever and the drive lever are firmly connected to the spring ends of a helical spring. A locking mechanism prevents the primary shaft from being able to be rotated into its end setting unless the delivery shaft also assumes the connect or disconnect setting, the locking mechanism being configured such that the delivery shaft is automatically rotated the last few degrees into the connect and disconnect setting of the primary shaft. This ensures that the connect and disconnect settings are reached when the helical spring is slackened in these settings. A disadvantage of this actuator is that it requires an intermediate shaft, since the primary and delivery shafts must have an opposite direction of rotation.
An actuator is further known from DE-AS 1 236 632, in which the primary shaft and the delivery shaft are disposed, however, coaxially to each other. The spring-loading arrangement includes two coaxial helical springs under bending stress, in the disconnect direction only the one spring being active, whereas in the connect direction both are active, so that different drive energies are available depending upon the switching direction. If, in the disconnection operation, the delivery shaft, after the locking setting of the primary shaft has been crossed, should fail to move under the action of the spring-loading arrangement, then an enforced coupling between these shafts is brought about. A further enforced coupling ensures, in the connection operation, that the delivery shaft is brought fully into the connect setting. This actuator has a considerable structural depth in the direction of the shafts.